ALT Test
At a Glance
Why Get Tested?
To screen for liver disease
When to Get Tested?
If your doctor thinks that you have symptoms of a liver disorder
Sample Required?
A blood sample taken from a vein in your arm
The Test Sample
What is being tested?
ALT is an enzyme found mostly in the liver; smaller amounts are also found in the kidneys, heart, and muscles. Under normal conditions, ALT levels in the blood are low. When the liver is damaged, ALT is released into the blood stream, usually before more obvious symptoms of liver damage occur, such as jaundice (yellowing of the eyes and skin).
How is the sample collected for testing?
A blood sample will be taken from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
The ALT test detects liver injury. ALT values are usually assessed along with the values found for other enzymes, such as alkaline phosphatase (ALP) and aspartate aminotransferase (AST), to help determine which form of liver disease is present.
When is it requested?
A doctor usually requests an ALT test with other laboratory investigations to evaluate a patient who has symptoms of a liver disorder. Some of these symptoms include jaundice, dark urine, nausea, vomiting, abdominal swelling, unusual weight gain, and abdominal pain. ALT can also be used, either by itself or with other tests, for:
- persons who have a history of known or possible exposure to hepatitis viruses,
- those who drink too much alcohol,
- those whose family have a history of liver disease,
- people who take drugs that might damage the liver.
In people with mild symptoms, such as tiredness or loss of energy, ALT may be tested to make sure they do not have chronic (long-term) liver disease. ALT is often used to monitor the treatment of persons who have liver disease, to see if the treatment is working, and may be ordered either by itself or along with other tests.
What does the test result mean?
Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute (short-term) hepatitis, often due to a virus infection. In acute hepatitis, ALT levels usually stay high for about 1–2 months, but can take as long as 3–6 months to return to normal.
ALT levels are usually not as high in chronic hepatitis, often less than 4 times the highest normal level: in this case, ALT levels often vary between normal and slightly increased, so doctors will order the test frequently to see if there is a pattern. In some liver diseases, especially when the bile ducts are blocked, when a person has cirrhosis, and when other types of liver cancer are present, ALT may be close to normal levels.
Is there anything else I should know?
An injection of medicine into the muscle tissue, or strenuous exercise, may increase ALT levels.
Certain drugs may raise ALT levels by causing liver damage in a very small percentage of patients taking the drug. This is true of both prescription drugs and some 'natural' health products. If your doctor finds that you have a high ALT, tell him or her about all the drugs and health products you are taking.
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
